Many media stories brought to the public's attention that fluorescent lights contain elemental mercury, which is a toxic metal. This raises a question about potential harm within your home and the homes of your customers if a CFL is accidentally broken. Does a broken CFL pose a significant risk of exposure to elemental mercury?

Exposure Risk

EPA states that the risk from exposure to elemental mercury is related primarily to the risk of inhaling mercury vapor. It is important to realize that we are always exposed to a basic background level of elemental mercury. In the United States, the level of elemental mercury in the outdoor air varies from 2 to 10 nanograms per cubic meter (ng/m3) of air. A nanogram is equal to 1 billionth of a gram. EPA sets the Reference Concentration (RfC) for exposure to elemental mercury at 300 ng/m3. This is EPA's best estimate, based on current research and risk assessment calculations, of exposure to mercury in the air that does not impose a significant risk to human health over the subject's lifetime. This estimate includes sensitive subgroups, such as children, infants, and pregnant women. The RfC provides guidance to homeowners concerning the risk of long-term exposure to mercury. What about short-term, but relatively high, exposure levels? The Occupational Safety and Health Administration (OSHA) sets the current permissible exposure level (PEL) for mercury vapor in the workplace at 100,000 ng/m3. This means that a worker should not be exposed to more than this level of mercury vapor even for a very short period of time.

What about short-term, but high, exposure outside the workplace? There are no published data on this topic. Therefore, there is no guidance for homeowners on what constitutes short-term, relatively high exposure risk. And the release of mercury vapor from a broken CFL would create a short-term exposure. This raises an important question. Just how high is the typical short-term exposure to mercury from a broken CFL? Findings of a study conducted by the Maine Department of Environmental Protection (Maine DEP) in 2007 helped to answer that question.

Choosing fluorescent lighting means purchasing and using lights that contain a small amount of elemental mercury. But doing so reduces the total amount of mercury in the environment.

Maine DEP investigators monitored the levels of elemental mercury in the air when CFLs were broken in a room with a floor area of 11 feet 4 inches x 12 feet 1 inch, and a 10-foot ceiling — a room similar in size to the average bedroom. There were windows on three sides of the room, and one of these, measuring 30 inches x 38 inches, was opened for the tests described below. The broken pieces were removed in a sealed container from the room, but the floor was not vacuumed, according to the existing Maine DEP guidelines for cleanup of broken CFLs. (Vacuuming just spreads the mercury vapor.)

New CFLs from seven different manufacturers, and of various wattages, were broken to measure the amount of mercury vapor released. A total of 35 new CFLs were smashed with a hammer over three types of flooring: wood flooring, short-pile carpeted flooring, and long-pile (shag) carpeted flooring. (See "Does It All Go into the Air?" for information about the percentage of mercury released as vapor.) New CFLs were used to obtain the highest possible air concentration of mercury, because new CFLs contain more mercury than used CFLs. Immediately after each break, air concentrations of elemental mercury were measured. Mercury measurements were taken at 1 foot and 5 feet directly above the breakage spot. The 1-foot height represents the breathing zone of a crawling infant. The 5-foot height represents the breathing zone of the typical adult.

Researchers measured at 1 foot and 5 feet above the floor the initial spike in mercury concentrations immediately after each CFL was broken. They then measured mercury concentrations at both heights at intervals of five seconds for a period of one hour immediately following the break. The readings were averaged to obtain a mercury air concentration over a one-hour period. The results are shown in Table 1.

Table 1. Maine DEP Study of Broken CFLs

Worst-Case Breakage Scenarios

The average mercury concentrations listed in Table 1 are 2,523 ng/m3 and 19,318 ng/m3 for the initial spike at 5 feet and 1 foot above the floor, respectively. Both of these readings are well above the EPA RfC for chronic exposure to elemental mercury of 300 ng/m3. And after a one-hour period, mercury concentrations remained above the RfC of 300 ng/m3, at 733 ng/m3 and 940 ng/m3 respectively. But keep in mind that the EPA RfC is for lifetime exposure, not for a spike in exposure lasting just one hour.

What about short, but relatively high, exposures? For these, the OSHA PEL is 100,000 nag/m3. Average concentrations shown in Table 1 are nowhere near this threshold. In fact, for 34 out of 35 breakage scenarios, none of the spikes — even at the 1-foot level — approached the OSHA PEL.

Worst-Case Scenario

In a worst-case breakage scenario designed by the Maine researchers, a 26W CFL was smashed over carpet. No ventilation was provided to the room, and only the larger pieces of the broken CFL were picked up. Those pieces were not removed from the room, but were placed in a trash can located within the room. Smaller pieces of the broken CFL were then cleaned up using a vacuum with a beater attachment.

In short, everything possible was done to elevate the air concentration of mercury in the room. Even with all this, the one-hour average air concentration of mercury was 21,262 ng/m3 at 1 foot above the floor and 16,814 ng/m3 at 5 feet above the floor, well below the OSHA PEL of 100,000 ng/m3. See Table 2.

Does It All Go into the Air?

Many people seem to think that when a CFL is switched on, all the mercury contained in that CFL is in vapor form. For example, if the average CFL contains 4 mg of elemental mercury (as was the case in 2007), they assume that when the lamp is switched on, 4 mg of mercury is in vapor form in the lamp. They further assume that if the lamp is broken while it is on, 4 mg of mercury will be released into the atmosphere. But this is not the case. Scientists from the Lighting Research Group at Lawrence Berkeley Laboratory studied the release of mercury from CFLs in 1993. They found that if the average CFL contains
5 mg of mercury, just 50 - 350 nanograms of mercury will be in vapor form when the lamp is on. More recent research has shown that much of the mercury contained in a fluorescent lamp is not released when the lamp is broken or landfilled. It attaches to the lamp walls, phosphor powder, and other components within the lamp.

Some Perspective

As data from the Maine DEP study illustrate, long-term exposure to mercury from a broken CFL poses a minuscule risk — and no risk at all if simple cleanup guidelines are followed.

And choosing incandescent lighting — although it eliminates the risk of exposure to elemental mercury — entails the risk of an even more potent and widespread form of mercury poisoning. We refer to methylmercury poisoning, which comes from eating fish. It is well known that fish — taken from both fresh and salt water — contain significant amounts of methylmercury. The FDA warns "women who might become pregnant, women who are pregnant, nursing mothers, and young children" to eat no more than 6 oz of albacore tuna per week, because it typically contains high levels of methylmercury.

Methylmercury is much more toxic than elemental mercury. After elemental mercury in the air is deposited in oceans, lakes, and other bodies of water, aquatic microorganisms biotransform it to methylmercury. When methylmercury is in the human body, it mimics the essential amino acid methionine. This mimicry allows methylmercury to move throughout the human body and to pass through the blood-brain barrier and into the placenta. Fetal exposure to methylmercury results in irreversible damage to the nervous system and neurodevelopmental toxicity. Adults and children can also experience neurodevelopmental problems from methylmercury exposure, although it is not certain whether low-dose exposure to adults is toxic.

Choosing fluorescent lighting means purchasing and using lights that contain a small amount of elemental mercury. But doing so reduces the total amount of mercury in the environment.

The likely dose of methylmercury from eating a 6 oz portion of albacore tuna is about 63,344 ng. A 2 oz portion would contain about 21,448 ng of methylmercury. Looking at Table 1 you can see that the average spike in elemental mercury concentrations immediately following, and just 1 foot above, a broken — and properly, promptly, and completely cleaned up — CFL is 19,318 ng/m3. Therefore, eating just a 2 oz portion of albacore tuna would result in a higher exposure to a more toxic form of mercury than being 1 foot above a CFL at the very moment it is broken, and inhaling every nanogram of elemental mercury following the break. We make this point to provide some perspective on mercury exposure risks, and to point out that eating fish is currently the primary way that most of us are exposed to mercury.

Choosing fluorescent lighting means purchasing and using lights that contain a small amount of elemental mercury. But doing so reduces the total amount of mercury in the environment. It's counterintuitive, but true. Since most electricity in the United States is produced from coal-fired electric plants, and since those plants are the primary source of mercury in the atmosphere, reducing electricity consumption will reduce our atmospheric load of mercury. Fluorescent lights use 75% less electricity than incandescent lights. Decreasing the amount of coal that is burned to power inefficient incandescent lighting will decrease mercury emissions into the environment. This will reduce the amount of methylmercury in our lakes, streams, and oceans. And this, in turn, will reduce the amount of methylmercury contained in the fish we eat.

As part of the 1999 - 2010 National Health and Nutrition Examination Survey conducted by the Centers for Disease Control, a large sample of humans were tested to determine blood-level concentrations of methylmercury. Results of the survey are online at www.cdc.gov/nchs/nhanes.htm.

Final Thoughts

In 2007, when the Maine DEP study was conducted, CFLs contained an average of 4 mg of mercury. But even then, some manufacturers were producing CFLs that contained as little as 1.5 mg of mercury. Maine DEP researchers noted that when they broke a CFL with lower mercury content, it produced lower air mercury concentrations. This is important information for consumers, because there are currently CFLs available that contain as little as 1 mg of mercury. The Federal Trade Commission recently announced that beginning in 2012 CFL labels and the bulbs themselves must specify mercury content. Therefore consumers who wish to limit exposure to mercury if they accidentally break a CFL can purchase CFLs with low levels of mercury. (For a list of manufacturers, see "learn more.")

For consumers who just cannot bring themselves to use fluorescent lighting in their homes, screw-based LED lights for use in incandescent fixtures are now available. On average, LEDs are 1.5 to 2 times as efficient as CFLs and 6 to 10 times as efficient as incandescents. They also last up to 25,000 hours. Purchasing LED lights enables consumers to maintain a zero risk of exposure to mercury from a broken fluorescent. It also reduces the total load of mercury in the atmosphere. Currently LEDs are fairly expensive to purchase, but prices are expected to decrease as more manufacturers enter the market.

Mark Pierceis an extension associate in the Department of Design and Environmental Analysis andJoseph Laquatrais a professor in the Department of Design and Environmental Analysis at Cornell University.

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